Create GreetingsController.java (#11057)

* Create GreetingsController.java

add controller to test the content type being set properly or not

* add unit tests for greetings controller

* update to avoid PMD violation

* correct the file type

* Update GreetingsControllerUnitTest.java

fix some imports & correct the names

* Update GreetingsControllerUnitTest.java

update the unit case to avoid internal server error for junit

spring-web-modules/spring-mvc-basics-4/src/main/java/com/baeldung/controller/controller/GreetingsController.java

@@ -0,0 +1,49 @@
+package com.baeldung.controller.controller;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
+import org.springframework.stereotype.Controller;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestMethod;
+import org.springframework.web.bind.annotation.ResponseBody;
+
+@Controller
+public class GreetingsController {
+    
+    @RequestMapping(
+        value = "/greetings-with-response-body", 
+        method = RequestMethod.GET, 
+        produces="application/json"
+    ) 
+    @ResponseBody
+    public String getGreetingWhileReturnTypeIsString() { 
+        return "{\"test\": \"Hello using @ResponseBody\"}";
+    }
+        
+    @RequestMapping(
+        value = "/greetings-with-response-entity",
+        method = RequestMethod.GET, 
+        produces = "application/json"
+    )
+    public ResponseEntity<String> getGreetingWithResponseEntity() {
+        final HttpHeaders httpHeaders= new HttpHeaders();
+        httpHeaders.setContentType(MediaType.APPLICATION_JSON);
+        return new ResponseEntity<String>("{\"test\": \"Hello with ResponseEntity\"}", httpHeaders, HttpStatus.OK);
+    }
+    @RequestMapping(
+        value = "/greetings-with-map-return-type", 
+        method = RequestMethod.GET, 
+        produces = "application/json"
+    )
+    @ResponseBody
+    public Map<String, Object> getGreetingWhileReturnTypeIsMap() {
+        HashMap<String, Object> map = new HashMap<String, Object>();
+        map.put("test", "Hello from map");
+        return map;
+    }
+}